refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/app/features/tasks/deps.py

@@ -1,6 +1,7 @@
 """Tasks feature 依赖：提供 get_tasks_service。"""
 
 from app.features.tasks.service import TasksService
+from app.core.deps_types import DbDep
 
 
 def get_tasks_service() -> TasksService:

api/app/features/tasks/router.py

@@ -8,6 +8,7 @@ from fastapi import APIRouter, Depends
 from pydantic import BaseModel
 
 from app.core.dependencies import get_current_user
+from app.core.openapi import error_responses
 from app.features.tasks.deps import get_tasks_service
 from app.features.tasks.service import TasksService
 from app.features.user.models import User
@@ -15,7 +16,7 @@ from app.features.user.models import User
 router = APIRouter(
     prefix="/api/tasks",
     tags=["tasks"],
-    responses={401: {"description": "认证失败"}},
+    responses=error_responses(401),
 )